We remind that generally the CSFE in a `clean' unpolarized quantum Hall system, being a collective excitation from the \(S\!=\!0\)  ground state, is a \(S\!=\!1\)  triplet characterised by 2D momentum \({\bf q}\) . The three components of the triplet differ by the values of spin quantum number \(S_z=-1,0,1\) , thus being energetically gapped by Zeeman energy \(|g\mu _BB|\) .[1]}, [2]}, [3]} The lowest-energy excitation in GaAs quantum Hall systems corresponds to the \(S_z=1\)  component and conventionally represents promotion of an electron from the fully occupied zeroth Landau level upward to the first one with a simultaneous spin flip from \(s_z=-1/2\)  to \(s_z=1/2\) . The energy of this CSFE component can be calculated in terms of expansion over ratio
\(r_s\!=\!E_{\rm C}/\hbar \omega _c\) 
of characteristic Coulomb energy \(E_{\rm C}\)  to cyclotron energy
\(\hbar \omega _c\)  (Refs. ka84, di05). In the case of ideally two-dimensional electrons the \(E_{\rm C}\) 
value would be equal to \(e^2/\kappa l_B\)  (\(\kappa \)  is the dielectric
constant, \(l_B\)  the magnetic length), however, in a modern GaAs wide-thickness quantum well \(E_{\rm C}\)  is considerably smaller. The CSFE energy counted off the ground-state level is determined by formula
\({E}_{\bf q}=\delta ^{(0)}+{\cal E}_{q},\) 
